Cryogenic liquids, such as nitrogen, hydrogen, and liquid oxygen, are typically stored in vacuum-jacketed cryogenic storage tanks. Traditional systems and methods for pumping cryogenic liquid from storage tanks often use liquid pumps housed in a vacuum jacketed sump (e.g., a mini-vacuum jacketed tank outside of the main cryogenic storage tank). Housing a liquid pump in a vacuum jacket, however, increases the cost of pumping operations and is a heat leak. Moreover, many of the current pumps must remain submerged during pumping operations to keep cool and lubricated. While some of the more recent pumps are self-cooling and self-lubricating (e.g., from the cryogenic liquid they pick up and discharge), they are very expensive and businesses and other enterprises operating cryogenic liquid pumps often prefer the older technology—the older submerged pumps are less expensive than the newer pumps and will likely be used extensively at least until the price of the newer pumps fall.
In general, current pump systems are installed using one of three methods. First, a pump may be installed inside an insulated, ASME pressure vessel sump outside of a cryogenic storage tank (e.g., the main storage/supply vessel). Although vacuum-jacketed lines may be run to and from the sump, other components of the sump configuration (e.g., valves, recirculation lines, vent lines, safety relief circuits, sump lid, etc.) often are not vacuum jacketed or otherwise insulated. As such, the sump configuration is not thermally efficient. In addition, insulated lines can be expensive, especially vacuum-jacketed insulated lines.
Second, a pump may be installed inside of a storage tank by mounting the pump to the bottom of the storage tank in a horizontal or vertical orientation. Because most conventional pumps (other than the self-cooling and self-lubricating pumps recently introduced) must remain submerged in cryogen to be cooled and lubricated, current horizontal and vertical arrangements require several inches of cryogenic liquid to be left in the storage tank to keep conventional pumps submerged. For example, a horizontal arrangement often requires a minimum level of at least 12″ of cryogenic liquid to remain in the storage tank to keep a pump, such as a 10″ diameter pump, submerged. As another example, a vertical arrangement often requires a level of cryogenic liquid in the storage tank equal to the level of the length of the pump. As a result, neither arrangement is efficient for traditional pump systems, as an operator of the pump is prevented from draining all of the cryogenic liquid from the storage tank, which in turn may result in a transportable storage tank carrying a large heel of product that cannot be dispensed or sold. In addition, any repair, replacement, or other maintenance of a traditional pump system may require a service person to drain, purge, warm, and enter into the tank, which may present safety hazards. Doing so also may take multiple days and require confined space entry procedures to be followed for the service person to enter the storage tank via a manway, for example, to remove an old pump and install a new or remanufactured pump.
Third, some very large storage tanks have incorporated a column in the design that extends from the manway opening to near the bottom of the storage tank and for which a pump may be positioned within. The column may be isolated from the rest of the storage tank and may include a foot valve in the bottom of the column. The pump may be configured to (or may use other means to) open the foot valve when the pump is lowered into the column and/or close the foot valve when the pump is removed. Thus, means to raise and lower the pump to open and close the foot valve before the manway is removed may be required; means to actuate the foot valve and raise or lower the pump may be required to be able to initially actuate or raise or lower the pump from outside the storage tank through the manway and/or vacuum jacket with any leakage. Replacing a pump in such a storage tank requires the column to be drained and purged and may also require the storage tank pressure to be vented down to zero; the storage tank may not need to be drained. For example, the column itself may need to be drained once the foot valve closes after removing the pump. As a result, the column also may require a positive pressure nitrogen purge to prevent moist humid air from entering into the column and forming frost on the cold walls of the column. In addition, the foot valve technology needs to be fool proof to seal off the cryogen in the vessel.
Conventional vacuum-jacketed cryogenic storage tanks with accessible manways typically employ a single manway lid. Transportable cryogenic storage tanks often include an inner splash plate suspended a few inches from the bottom inner surface of the manway to prevent cryogenic liquid from splashing up onto an uninsulated manway lid (it is common practice for manufacturers of transportable cryogenic storage tanks to employ such a feature). While some of the current cryogenic storage tanks employ two manway lids, such as an inner manway lid and an outer manway lid, current outer manway lids merely serve as an “environmental seal” (e.g., only operable to keep humid air out the manway). Manufacturers of such storage tanks may include conventional cryogenic service fiberglass insulation and multi-layered super insulation radiant barriers in the space between the two manway lids (e.g., the manway).